Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
A smooth evacuated cavity inside a volume of liquid medium is an essential part of a plasma compression system that is in development at General Fusion Inc., in Burnaby, Canada. The evacuated cavity or also called vortex cavity is created in a center of a plasma compression vessel filled with a molten metal, such as a molten lead-lithium. A pumping system is used to provide a rotational flow of the fluid in the compression vessel and create the cavity which can be gas or vacuum cavity. Plasma is injected into such cavity and is then compressed with a converging pressure wave that collapses the cavity compressing the plasma therein.
Prior experiments have been conducted using water and/or liquid lead pumping systems to produce a vortex cavity. The pumping system in some of these systems was based on a concept of a bath tub vortex in which a cavity is formed as a result of tangential pumping of the liquid into a compression vessel and draining the liquid out from a hole on the bottom of such vessel. Even though such systems were successful in forming the vortex cavity, problems have been identified, such as for example, a case where the cavity extends over the entire vessel and enters into a draining pipe, such that the obtained vortex cavity was lacking a desired smoothness of the liquid/gas interface. The lack of smoothness of the interface, i.e. a persistent existence of the high-frequency surface ripples, has been attributed to a presence of strong vertical shear layers in the vicinity of the interface as well as interaction of the rotating interface (top and bottom of the vortex) with stationary walls of the vessel. The vortex cavity extends over the entire height of the vessel, touching the stationary wall at the top of the vessel and entering the drainage hole at the bottom of the vessel. When the vortex cavity extends into a drainage hole, it may block a significant part of the drainage area which can result in a significant increase in the vertical velocity (and shear) near the vortex interface which in turn can lead to destabilizing (e.g. precession) of the vortex and poor quality of its surface. In addition to this, the amount of fluid in the system cannot be fixed, i.e. fluid injection and fluid drainage are decoupled (open system), leading to a difficulty in controlling and/or predicting the exact parameters of the generated vortex cavity.